1. Field of the Invention
The invention relates to a method of removing organic-containing materials such as photoresists, high temperature organic layers, and organic dielectric materials from a substrate surface of a flat panel display or solar cell array or other large scale substrate (a substrate which is typically larger than about 0.5 meter by 0.5 meter).
2. Brief Description of the Background Art
The information in this Background Art portion of the application is provided so that the reader of the application can better understand the invention which is described subsequently. The presence of information in this Background Art portion of the application is not an admission that the information presented or a that a combination of the information presented is prior art to the invention.
The fabrication of electronic device structures is complicated by the number of different materials which are used, both to provide the elements of the functional device, and as temporary process structures during fabrication of the device. Since most of the devices involve the formation of layers of inter-related, intricate, patterned structures, photoresists and high temperature organic masking materials are commonly used during patterning of underlying layers of material which are present over large area (typically about 0.25 m2 or greater) surfaces. A patterned photoresist is one of the temporary processing structures and must be removed once work on the underlying structure through openings in the photoresist is completed. Therefore, there is a need for an efficient and inexpensive method of removing, stripping, or cleaning of organic photoresists, as well as other organic layer residues, from large substrate surfaces. Due to the varying composition of a substrate underlying a photoresist, for example, it is important that a method used to remove the photoresist not be reactive with (corrosive to) surfaces underlying the photoresist. One problem has been the presence of metallic materials and the tendency of these materials to oxidize and dissolve the oxidized layer.
To be useful in processing of large surface areas, it is helpful to have the stripping and cleaning material be a non-corrosive fluid. The fluid should be minimally affected by the presence of an ambient atmospheric condition. It is also helpful when the removal process can be carried out at room temperature, or at least below about 80° C. Finally, it is always desirable that the fluid used for removal of the organic material be environmentally friendly.
In order to remove an organic material such as a photoresist for example, and specifically to strip photoresist from large substrate surfaces, a number of techniques have been used. Representative techniques for removing photoresists, as well as their advantages and disadvantages, are described below.
A Piranha solution, which consists of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2), typically in a volumetric ratio of 4:1, works well for photoresist removal, but cannot be used on substrate surfaces which include exposed metal, because it will etch the metal. Also, because it is very viscous, the Piranha solution is difficult to rinse off a substrate surface after a photoresist removal process. Further, the H2SO4/H2O2 solution cannot be recovered or re-used many times, as it decomposes rapidly. Finally, the solution needs to be applied at relatively high temperatures of at least 70° C., and typically about 120° C.
Several other techniques for removal of organic photoresists are based on the use of organic solvent-based strippers, such as monoethanolamine (MEA), dimethylsulfoxide (DMSO), n-methylpyrrolidone (NMP), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, and methylethylketone (MEK). Unlike the Piranha solution, these organic solvent strippers can be used when metals are present. However, these organic solvent strippers cannot be easily recovered after saturation with dissolved photoresist, because the photoresist is difficult to separate from the organic solvent. Therefore, the saturated organic solvent strippers must be disposed of, creating an environmental problem, or recovered for recycling using a distillation technique which is cumbersome and expensive. Like the Piranha solution, these solvents are typically heated prior to use, but to somewhat lower temperatures than the Piranha solution, typically around 50-65° C.
Japanese Patent Publication No. 59125760, of Tanno et al., published Jan. 10, 1986, describes dissolving ozone in an organic acid (such as formic acid or acetic acid) and using the ozonated organic acid to remove contamination from semiconductor substrates. Any heavy metal on the wafer is said to form a formate or an acetate, and any organic contaminant is decomposed by ozone, so that stains on the surface of the substrate can be removed.
T. Ohmi et al., in an article entitled “Native Oxide Growth and Organic Impurity Removal on Si Surface with Ozone-Injected Ultrapure Water” (J. Electrochem. Soc., Vol. 140, No. 3, March 1993), describe the use of ozone-injected ultrapure water to remove adsorbed organic impurities from a wafer surface prior to other wafer cleaning procedures. Ozone concentration in the water was 1-2 ppm. The process described by Ohmi et al. was said to be capable of effectively removing organic contaminants from the wafer surface in a short time at room temperature. Processing waste from the process was said to be simple, and the chemical composition of the ozone-injected ultrapure water was said to be easily controllable.
U.S. Pat. No. 5,464,480, issued Nov. 7, 1995, to Matthews et al., and entitled “Process and Apparatus for the Treatment of Semiconductor Wafers in a Fluid”, describes a process for removing organic materials from semiconductor wafers using chilled deionized water (1° C. -15° C.). The amount of ozone dissolved in the water is temperature-dependent. Lowering the temperature of the water is said to have increased the concentration of ozone in the water and to have increased the photoresist strip rate using the ozone/chilled water solution.
U.S. Pat. No. 5,632,847, issued May 27, 1997, to Ohno et al., and entitled “Film Removing Method and Film Removing Agent”, describes a method of removing a film (e.g., an organic or metal-contaminated film) from a substrate surface by injecting ozone into an inorganic acid aqueous solution (e.g., a mixed solution of dilute HF and dilute HCl) and bringing bubbles formed by the ozone injection into direct contact with the film. Each bubble is said to be composed of an inside ozone bubble and an outside acid aqueous solution bubble. The Ohno et al. reference recommends an acid aqueous solution of 5 weight % or less, kept at room temperature, where the ozone concentration is within a range from 40,000 ppm to 90,000 ppm. Ozone has also been dissolved in sulfuric acid for use in cleaning semiconductor surfaces, as described, for example, in U.S. Pat. Nos. 4,917,123 and 5,082,518.
U.S. Pat. No. 5,690,747, issued Nov. 25, 1997, to Doscher, and entitled “Method for Removing Photoresist with Solvent and Ultrasonic Agitation”, describes a method for removing photoresist using liquid organic solvents which include at least one polar compound having at least one strongly electronegative oxygen (such as ethylene diacetate) and at least one alicyclic carbonate (such as ethylene carbonate).
European Patent Publication No. 0867924, of Stefan DeGendt et al., published Sep. 30, 1998, and entitled “Method for Removing Organic Contaminants from a Substrate”, describes the use of an agent to remove the organic contaminants, where the agent comprises water vapor, ozone, and an additive acting as a scavenger. Use of a liquid agent comprising water, ozone, and an additive acting as a scavenger is also discussed. The additive is recommended to be an OH radical scavenger, such as a carboxylic or phosphoric acid or a salt thereof. Preferred examples are acetic acid and acetate, as well as carbonate and phosphate. Although carboxylic acids as a whole are mentioned, there is no data for any carboxylic acid other than acetic acid. The authors describe how the ozone level of an aqueous ozone solution increases upon the addition of acetic acid to the water-based solution. They also disclose that photoresist strip rate increases upon the addition of acetic acid to an aqueous ozone solution. This publication is incorporated by reference in its entirety.
U.S. Pat. No. 6,080,531, issued Jun. 27, 2000, to Carter et al., and entitled “Organic Removal Process” describes a method of photoresist removal in which a treating solution of ozone and bicarbonate (or other suitable radical scavenger) is used to treat a substrate for use in an electronic device. The concentration of bicarbonate ion or carbonate ion in the treating solution is said to be approximately equal to or greater than the ozone concentration. The method is said to be suited to removal of photoresist (as well as other organic materials) where metals such as aluminum, copper, and their oxides are present on the substrate surface.
Japanese Patent Publication No. 2002/025971, published Jan. 25, 2002, and assigned to Seiko Epson Corp. and Sumitomo Precision Prod. Co., teaches the use of ozonated water with acetic acid and ultraviolet radiation to remove photoresist. Ozonated water containing acetic acid is continuously supplied to the center portion of a rotating substrate. The ultraviolet rays from a UV lamp are irradiated onto the substrate to remove resist adhering to the surface of the substrate. The process is said to remove organic substances such as resist adhering onto the substrate without need for high temperature heat treatment.
U.S. Patent Application Publication No. 2002/0066717 A1, of Verhaverbeke et al., published Jun. 6, 2002, and entitled “Apparatus for Providing Ozonated Process Fluid and Methods for Using Same”, describes apparatus and methods for wet processing of electronic components using ozonated process fluids. Verhaverbeke et al. teach that it is desirable to have as high an ozone concentration as possible to achieve rapid cleaning of electronic components. Verhaverbeke et al. achieved ozone concentrations in water up to 300 g/m3 by using a closed vessel with recirculated ozonated liquid, which is supplied under pressure. Verhaverbeke et al. describe the use of various chemically reactive process fluids which may be used in combination with ozone, including inorganic acids, inorganic bases, fluorinated compounds, and acetic acid. The Verhaverbeke et al. reference also provides an overview of the literature on the use of ozonated deionized water for photoresist removal from electronic component surfaces. This published patent application is incorporated by reference in its entirety.
U.S. Patent Publication No. 2002/0173156 A1, of Yates et al., published Nov. 21, 2002, and entitled “Removal of Organic Material in Integrated Circuit Fabrication Using Ozonated Organic Acid Solutions”, describes the use of organic acid components to increase the solubility of ozone in aqueous solutions which are used for removing organic materials, such as polymeric resist or post-etch residues, from the surface of an integrated circuit device during fabrication. Each organic acid component is preferably said to be chosen for its metal-passivating effect. Such solutions are said to have significantly lower corrosion rates when compared to ozonated aqueous solutions using common inorganic acids for ozone solubility enhancement, due to a surface passivating effect of the organic acid component.
U.S. Pat. No. 6,551,409, issued Apr. 22, 2003, to DeGendt et al., and entitled “Method of Removing Organic Contaminants from a Semiconductor Surface”, describes a method for removing organic contaminants from a semiconductor surface, where the semiconductor is held in a tank which is filled with a gas mixture comprising water vapor and ozone. DeGendt et al. teach that the use of gas phase processing, where the substrate surface is contacted with an ozone/water vapor mixture, enables an increase in ozone concentration near the wafer surface.
U.S. Pat. No. 6,674,054, issued Jan. 6, 2004, to Boyers et al., and entitled “Method and Apparatus for Heating a Gas—Solvent Solution”, describes a method of quickly heating a gas—solvent solution from a relatively low temperature T1 to a relatively high temperature T2, such that the dissolved gas concentration at T2 is much higher than if the gas had originally been dissolved into the solvent at T2. The example of gas—solvent solution is an ozone gas in water solution. The objective is to heat a cold ozone—water solution using an in-line heater just prior to application of the solution to a substrate surface, to increase the reaction rate at the substrate surface. Table A in Col. 33 shows the solubility of ozone gas in water as a function of temperature and pressure. This '054 patent is incorporated by reference in its entirety.
U.S. Pat. No. 6,696,228, issued Feb. 4, 2004, to Muraoka et al., and entitled “Method and Apparatus for Removing Organic Films”, describes a method and apparatus for removing an organic film such as a resist film from a substrate surface using a treatment liquid which can be recycled and re-used. The treatment liquid is typically formed from liquid ethylene carbonate, liquid propylene carbonate, or a mixture thereof, and typically contains dissolved ozone. Since ethylene carbonate is a solid at room temperature, this photoresist removal method requires the use of elevated temperatures, in the range of about 50-120° C.
U.S. Pat. No. 6,699,330, issued Mar. 2, 2004, to Muraoka, and entitled “Method of Removing Contamination Adhered to Surfaces and Apparatus Used Therefor”, describes a method of removing surface-deposited contaminants from substrates for electronic devices. The method includes bringing an ozone-containing treating solution into contact with the surface of a treating target (such as a semiconductor substrate) on which contaminants have deposited. The ozone-containing treating solution comprises an organic solvent having a partition coefficient to ozone of 0.6 or more, where the partition coefficient refers to a partition or division of gaseous ozone between an organic solvent that is in a liquid phase at standard temperature and pressure and an inert gas in a gaseous phase which comes in contact with the organic solvent. Any organic solvents are said to be useful in the invention, so long as they provide the desired partition coefficient. Preferably organic solvents are fatty acids, including acetic acid, propionic acid, and butyric acid. Enabling embodiments are provided for acetic acid. Ozonated acetic acid is used in a closed system with a constant ozone partial pressure above the system to keep a high concentration of ozone in the acetic acid and to minimize evaporation of the acetic acid.
Although high concentrations (≧200 ppm) of ozone can be obtained in acetic acid, and ozonated acetic acid may provide a rapid photoresist strip rate (≧1 μm/min), there are major drawbacks to the use of ozonated acetic acid for photoresist removal. One of the primary considerations is corrosivity. The presence of acetic acid has been observed to cause corrosion in metals, in particular, copper and molybdenum. These metals are commonly used in the flat panel display industry. Further, acetic acid is a solid at temperatures below about 16.7° C., which can cause problems under some desired processing conditions.
In view of the above, there is a need for an improved method of stripping and cleaning organic materials from electronic device surfaces, particularly when metals are present. In particular, there is a need for a stripping and cleaning method which has universal applicability with respect to the surface composition of the substrate. Due to the common presence of metals in semiconductor device substrates, flat panel display substrates, and solar cell arrays, methods of stripping and cleaning organic materials which are harmful when metals are present are not attractive.
Further, with respect to the manufacture of large flat panel substrates (such as those used for AMLCD or AMOLED panels, and in some instances solar panels), there is a need for a stripping and cleaning solution that can be applied over a stationary object or on an object that is moving on a conveyor belt in an atmospherically exhausted environment.
In addition, it would be highly desirable if the stripping and cleaning solution could be re-used over multiple processing cycles, without the need for frequent replenishment or filtering of the solution. It would also be advantageous if such an improved method for the removal of organic materials could be performed at room temperature.